Method for producing ash-free coal

ABSTRACT

A method for producing ash-free coal includes: pulverizing a coal in the presence of a protection solvent; heating an extraction solvent; mixing pulverized matter obtained after the pulverizing, with the extraction solvent obtained after the heating; separating a solution containing a coal component dissolved therein, from a slurry obtained after the mixing; and evaporatively separating the protection solvent and the extraction solvent from the solution obtained after the separating.

TECHNICAL FIELD

The present invention relates to a method for producing ash-free coal.

BACKGROUND ART

Coal finds extensive use as fuels for thermal power generation or boilers, or as materials of chemical products. Thus, it has been strongly desired to develop techniques for efficiently removing ash from coal, as a measure for environmental preservation. Attempts to use ash-free coal (hyper coal) cleared of ash have been made as, for example, a substitute for liquid fuels such as LNG in high-efficiency combined-cycle generation systems driven by gas turbine combustion. Also, ash-free coal has been put to trial use as coking coal for steelmaking, such as cokes for use in blast furnaces.

It has been common practice to produce ash-free coal by: mixing a coal with a solvent to prepare a slurry; heating the slurry to allow soluble components of the coal to be dissolved in the solvent; recovering a solution containing the soluble components dissolved therein by solid-liquid separation; and evaporating the solvent contained in the solution to extract only the soluble components of the coal.

In regard to the production of ash-free coal, there have been demands that the production efficiency of ash-free coal be improved through increased yield by allowing a larger amount of components of coal to be dissolved in the solvent. To increase the yield of ash-free coal, a technique has been proposed that accelerates dissolution of components of coal by raising the temperature of the coal within a short time period through mixing a preheated solvent with the coal (see, for example, Japanese Unexamined Patent Application, Publication No. 2014-208757). It is inferred that the rapid rise in the temperature of coal weakens the bonds between molecules constituting the coal, and consequently accelerates dissolution of the components, which might be otherwise time-consuming.

However, even when mixed with the high-temperature solvent, a coal composed of large particles cannot be rapidly heated entirely to its central portion. In this regard, the aforementioned publication discloses the use of finely pulverized coals in which the weight proportion of coals having a grain size of less than 1 mm is greater than or equal to 80%.

The present inventors accordingly pulverized a coal into powder having a mean particle diameter of about 0.1 mm, in an attempt to improve the extraction rate. However, the coal pulverized into powder rather exhibited a lower extraction rate.

PRIOR ART DOCUMENT Patent Document

Patent Document 1: Japanese Unexamined Patent Application, Publication No. 2014-208757

SUMMARY OF THE INVENTION Problems to be Solved by the Invention

In view of such a circumstance, the present invention has an object to provide a method for producing ash-free coal that enables a relatively high rate of extraction from coal to be achieved.

Means for Solving the Problem

After a thorough investigation, the present inventors concluded that the coal increased in surface area through pulverization into powder, and was subjected accelerated aeration (oxidation) through increased contact with air accordingly, resulting in a decrease in components to be converted into ash-free coal and thus leading to a lower extraction rate. The present inventors therefore have accomplished the present invention in the expectation that pulverizing a coal without aeration would improve the extraction rate and increase the production efficiency of ash-free coal.

According to an aspect of the invention made for solving the aforementioned problem, a method for producing ash-free coal includes: pulverizing a coal in the presence of a protection solvent; heating an extraction solvent; mixing pulverized matter obtained after the pulverizing, with the extraction solvent obtained after the heating; separating a solution containing a coal component dissolved therein, from a slurry obtained after the mixing; and evaporatively separating the protection solvent and the extraction solvent from the solution obtained after the separating.

Due to involving pulverizing a coal in the presence of the protection solvent, the method for producing ash-free coal of the aspect of the invention enables the particle diameter of the coal to be reduced, while preventing or minimizing aeration of the coal through reduced contact with air. The method thus prevents or minimizes loss of components to be converted into ash-free coal, and enables the coal to be rapidly heated entirely to its central portion by the heat of the extraction solvent preheated in the mixing, thereby enabling a relatively high rate of extraction from coal to be achieved. Therefore, the method for producing ash-free coal achieves efficient production of ash-free coal.

The pulverized matter obtained after the pulverizing preferably has a mean particle diameter of 0.2 mm or less. When having a mean particle diameter of less than or equal to the upper limit, the pulverized matter obtained after the pulverizing is rapidly heated entirely to its central portion in the mixing, thereby enabling a relatively high rate of extraction from coal to be achieved. The term “mean particle diameter” as referred to herein means a particle diameter corresponding to 50% on the cumulative volumetric particle size distribution as measured by laser diffraction.

In the mixing, the pulverized matter is preferably mixed with the extraction solvent in such a manner that a temperature of the pulverized matter is e at a rate of 600° C./min or higher. Mixing the pulverized matter with the extraction solvent in the mixing in such a manner that the temperature of the pulverized matter is raised at a rate of temperature rise of 600° C./min or higher enables a higher rate of extraction from coal to be achieved more reliably. The “rate of temperature rise of the pulverized matter” as referred to herein means a value determined by dividing the temperature difference between a temperature-stabilized slurry and the pulverized matter unmixed with the extraction solvent, by the time between the start of the mixing and the instant when the temperature of the extraction solvent, i.e., the apparent temperature of the slurry, stabilized (the time needed for the internal temperature of the pulverized matter to conceivably reach the temperature of the extraction solvent).

The protection solvent and the extraction solvent are preferably identical solvents. After being separated and recovered in the evaporatively separating, the protection solvent and the extraction solvent that are identical solvents can be recycled as the protection solvent or the extraction solvent.

In the pulverizing, a content of the protection solvent is preferably greater than or equal to 20% by mass and less than or equal to 60% by mass. In the case where the content of the protection solvent in the pulverizing falls within the range, the total amount of the sensible heat of the protection solvent is reduced, and the amount of heat required for the extraction solvent in the mixing is regulated accordingly, while aeration is prevented more reliably during the pulverization.

Effects of the Invention

Therefore, the method for producing ash-free coal according to the aspect of the present invention enables a relatively high rate of extraction from coal to be achieved.

BRIEF DESCRIPTION OF THE DRAWING

FIG. 1 is a flowchart of a procedure for producing ash-free coal according to an embodiment of the present invention.

FIG. 2 is a graph showing the extraction rate and the particle diameter of coal for each of Example, Control Example and Comparative Examples of the present invention.

DESCRIPTION OF EMBODIMENTS

An embodiment of the present invention will be described in detail with appropriate references to the drawings.

Method for Producing Ash-Free Coal

With reference to FIG. 1, a method for producing ash-free coal includes: pulverizing a coal in the presence of a protection solvent (Step S1: Pulverizing Step); heating an extraction solvent (Step S2: Heating Step); mixing pulverized matter obtained after the pulverizing step, with the extraction solvent obtained after the heating step (Step S3: Mixing Step); separating a solution containing a coal component dissolved therein, from a slurry obtained after the mixing step (Step S4: Solution Separating Step); and evaporatively separating the protection solvent and the extraction solvent from the solution obtained after the separating step (Step S5: Evaporatively Separating Step).

Pulverizing Step

In Step S1, the pulverizing step is performed to pulverize a coal in the presence of the protection solvent, which covers the surfaces of pulverized coals to keep the surfaces (cross sections) exposed by the pulverization of the coal from contact with air (oxygen, in particular).

The pulverizing may be carried out by using, for example, a planetary mill, a ball mill, an impact mill, a ring rolling mill or a ball race mill.

Pulverizing a coal premixed with the protection solvent in the pulverizing step prevents aeration of the coal more reliably. Alternatively, a coal may be mixed with the protection solvent while being pulverized in a particular type of mills, such as a batch mill, so that the surfaces of coal particles are covered with the protection solvent.

The pulverizing step is preferably performed under an atmospheric pressure in light of equipment costs and energy costs. In the pulverizing step, the upper limit of the temperature of the coal and the protection solvent is preferably 100° C., more preferably 80° C., and still more preferably 50° C. Although the lower limit of the temperature of the coal and the protection solvent in the pulverizing step is not limited, cooling that would lead to unnecessary increases in cost is not preferred. In the case where the temperature of the coal and the protection solvent in the pulverizing step is greater than the upper limit, the bonds between molecules constituting the coal may not be weakened in the mixing step, resulting in insufficient improvement effect on the extraction rate.

The lower limit of the mean particle diameter of the pulverized matter obtained after the pulverizing step is preferably 0.01 mm, and more preferably 0.02 mm. The upper limit of the mean particle diameter of the pulverized matter obtained after the pulverizing step is preferably 0.2 mm, and more preferably 0.1 mm. In the case where the mean particle diameter of the pulverized matter is less than the lower limit, the improvement effect on the extraction rate produced by the pulverization of a coal into small particles may plateau, and this may lead to unnecessary increases in cost. Conversely, in the case where the mean particle diameter of the pulverized matter is greater than the upper limit, the improvement effect on the extraction rate may be insufficient.

The upper limit of the particle diameter corresponding to 90 on the cumulative volumetric particle size distribution of the pulverized matter obtained after the pulverizing step is preferably 0.5 mm, and more preferably 0.2 mm. The lower limit of the particle diameter corresponding to 90 on the cumulative volumetric particle size distribution of the pulverized matter obtained after the pulverizing step is not limited, and may be any value falling within the range of the mean particle diameter. In the case where the particle diameter corresponding to 90 on the cumulative volumetric particle size distribution of the pulverized matter is greater than the upper limit, the improvement effect on the extraction rate may be insufficient.

Coal

Coal feedstock according to the method for producing ash-free coal is not limited to particular coals, and may be coals of various ranks. For example, bituminous coal with a high extraction rate, or less expensive low-quality coals (subbituminous coal and lignite) may be suitably used. A combination of different types of coals may be used as coal feedstock. These coals may be dried beforehand by, for example, air-drying, or may contain the moisture when being used.

Protection Solvent

The protection solvent for covering the surfaces of coals in the pulverizing step may be any solvent that is miscible with the extraction solvent (described below) and removable through pyrolysis or evaporative separation in the evaporatively separating step. In particular, a solvent having a strong affinity for coals (capable of easily wetting coals) at normal temperature is preferred.

The upper limit of the kinetic viscosity of the protection solvent at 20° C. is preferably 100 mm²/s, and more preferably 10 mm²/s. The lower limit of the kinetic viscosity of the protection solvent at 20° C. is not limited. In the case where the kinetic viscosity of the protection solvent at 20° C. is greater than the upper limit, films formed of the protection solvent may be likely to get ripped on the surfaces of coals, failing to sufficiently prevent aeration of the coals. It is to be noted that the term “kinetic viscosity” as referred to herein means a value measured in accordance with JIS-K2283 (2000).

Examples of the protection solvent include: monocyclic aromatic compounds such as benzene, toluene and xylene; bicyclic aromatic compounds such as naphthalene, methylnaphthalene, dimethylnaphthalene and trim ethylnaphthalene; and the like.

The protection solvent may contain additives such as a surfactant for improving wettability of coal. Additives that will be pyrolyzed in the mixing step or the evaporatively separating step are preferred for easy recycling of solvents.

In the pulverizing step, the lower limit of the content of the protection solvent (the proportion of the protection solvent in the mixture of the coal and the protection solvent) on a dry ash-free basis (daf) is preferably 20% by mass, and more preferably 30% by mass. The upper limit of the content of the protection solvent in the pulverizing step is preferably 60% by mass, and more preferably 50% by mass. In the case where the content of the protection solvent in the pulverizing step is less than the lower limit, the protection solvent may fail to cover the surfaces of coals, and consequently, may fail to sufficiently prevent aeration of the coals. In addition, such a solvent may impart poor fluidity to the pulverized matter, making it less easy to handle. Conversely, in the case where the content of the protection solvent in the pulverizing step is greater than the upper limit, a greater amount of heat may be required for the solvent in the mixing step (described below) to offset the sensible heat load of the protection solvent, leading to unduly low production efficiency of ash-free coal.

The pulverized matter obtained in the pulverizing step is preferably pasty, for improved handleability in the mixing step (described below). The lower limit of the viscosity of the pulverized matter in the form of a paste at 30° C. is preferably 0.5 Pa.s, and more preferably 1 Pa. s. The upper limit of the viscosity of the pulverized matter in the form of a paste is preferably 1,000 Pa.s, and more preferably 600 Pa.s. In the case where the viscosity of the pulverized matter in the form of a paste is less than the lower limit, the proportion of the protection solvent in the pulverized matter in the form of a paste may be excessively large, and thus, the rate of temperature rise in the mixing step (described below) may not be high enough for producing sufficient improvement effect on the extraction rate. Conversely, in the case where the viscosity of the pulverized matter in the form of a paste is greater than the upper limit, the pulverized matter in the form of a paste may be less easy to handle.

Heating Step

In Step S2, the heating step is performed to preheat the extraction solvent. A heating process of the extraction solvent is not limited, and for example, in-line heating by a heat exchanger may be performed. The heat exchanger may be of, for example, the multitubular, plate or spiral type.

Extraction Solvent

The extraction solvent is not limited, and may be any solvent in which coal can be dissolved. Examples of the extraction solvent include: monocyclic aromatic compounds such as benzene, toluene and xylene; bicyclic aromatic compounds such as naphthalene, methylnaphthalene, dimethylnaphthalene and trimethylnaphthalene; and the like. Of these, coal-derived bicyclic aromatic compounds such as methylnaphthalene and naphthalene, which are oils obtained by distilling oils being by-products of carbonizing coal in coke production, are suitably used. The bicyclic aromatic compounds have a basic structure similar to that of structural molecules of coal, and thus have a strong affinity for coal. This feature enables a relatively high extraction rate to be achieved.

The extraction solvent and the protection solvent are preferably identical solvents. After being separated and recovered in the evaporatively separating step (described below), the protection solvent and the extraction solvent that are identical solvents can be recycled as the protection solvent and the extraction solvent directly, thereby leading to a reduction in the cost of ash-free coal production.

The boiling point of the extraction solvent is not limited. For example, the lower limit of the boiling point of the extraction solvent is preferably 180° C., and more preferably 230° C. The upper limit of the boiling point of the extraction solvent is preferably 300° C., and more preferably 280° C. In the case where the boiling point of the extraction solvent is below the lower limit, the recovery rate of the extraction solvent may be low due to a great loss of the extraction solvent to be recovered in the evaporatively separating step (described below). Conversely, in the case where the boiling point of the extraction solvent is above the upper limit, the solvent-soluble components may be less separable form the extraction solvent, and the recovery rate of the extraction solvent may be low as in the above case.

The lower limit of the temperature of the heated extraction solvent is preferably 330° C., and more preferably 380° C. The upper limit of the temperature of the heated extraction solvent is preferably 450° C., and more preferably 430° C. In the case where the temperature of the heated extraction solvent is below the lower limit, the extraction solvent may fail to sufficiently raise the temperature of the pulverized coals in the mixing step (described below), resulting in an insufficient extraction rate. Conversely, in the case where the temperature of the heated extraction solvent is above the upper limit, pyrolysis radicals generated in pyrolytic reactions of coal in the mixing step may recombine, also resulting in a low extraction rate.

Mixing Step

In Step S3, the mixing step is performed to mix the pulverized matter including the protection solvent having been blended therein in the pulverizing step, with the extraction solvent having been heated to high temperatures in the heating step, thereby rapidly raising the temperatures of the individual coal particles in the pulverized matter. This step provides a slurry containing coal particles dispersed in the extraction solvent.

In the mixing step, the lower limit of the rate of temperature rise of the pulverized matter is preferably 600° C./min, and more preferably 1,000° C./min. The upper limit of the rate of temperature rise of the pulverized matter in the mixing step is not limited, and is preferably 200,000° C./min, and more preferably 100,0000° C./min. In the case where the rate of temperature rise of the pulverized matter in the mixing step is below the lower limit, sufficient improvement effect on the extraction rate, which might be otherwise produced by a rapid temperature rise, may not be achieved. Conversely, in the case where the rate of temperature rise of the pulverized matter in the mixing step is above the upper limit, throughput may be excessively regulated, and/or the equipment cost may be unduly increased.

Examples of the process for mixing the pulverized matter with the extraction solvent include a process that involves, as disclosed in Japanese Unexamined Patent Application, Publication No. 2014-208757, pressurizing and feeding the pulverized matter by a lock hopper, into a pipe through which an extraction solvent is flowing. As an alternative to the lock hopper, a pump or another feeding unit may be used to feed the pulverized matter into a pipe.

The lock hopper is used in the following manner. The pulverized matter in the form of a paste is fed into the hopper, which can be internally pressurized by supply of gas. Then, the hopper is closed and supplied with gas so as to be internally pressurized, whereby the pulverized matter in the form of a paste is squeezed out by the force of the gas. The lock hopper may be part of a pipe partitioned by two valves.

Examples of the pump that may be used as the feeding unit include a mohno pump, a sine pump, a diaphragm pump, a bellows pump and a rotary pump.

For mixing the pulverized matter with the extraction solvent, the pulverized matter may be fed all at once into a tank equipped with a mixer having a sufficient mixing power and retaining the extraction solvent. Alternatively, the extraction solvent may be fed all at once into a tank containing the pulverized matter, and may be stirred in the tank.

The lower limit of the ratio of the mass of the extraction solvent mixed with the pulverized matter to the mass of coal in the pulverized matter is preferably 2, and more preferably 3. The upper limit of the ratio of the mass of the extraction solvent mixed with the pulverized matter to the mass of coal in the pulverized matter is preferably 10, and more preferably 8. In the case where the ratio of the mass of the extraction solvent mixed with the pulverized matter is less than the lower limit, the coal components may not be sufficiently extracted. Conversely, in the case where the ratio of the mass of the extraction solvent mixed with the pulverized matter is greater than the upper limit, the solution may contain ash-free coal components in small concentrations, leading to unduly low production efficiency.

The lower limit of the ratio of the mass of the extraction solvent mixed with the pulverized matter to the mass of the protection solvent in the pulverized matter is preferably 3, and more preferably 4. The upper limit of the ratio of the mass of the extraction solvent mixed with the pulverized matter to the mass of the protection solvent in the pulverized matter is preferably 15, and more preferably 12. In the case where the ratio of the mass of the extraction solvent to the mass of the protection solvent is less than the lower limit, the rate of temperature rise of pulverized coals may not be high enough due to the sensible heat load in the heating of the protection solvent. Conversely, in the case where the ratio of the mass of the extraction solvent to the mass of the protection solvent is greater than the upper limit, the solution may contain ash-free coal components in small concentrations, leading to unduly low production efficiency.

The lower limit of the temperature of a slurry (i.e., the temperature of pulverized coals) obtained after the mix step is preferably 300° C., and more preferably 350° C. The upper limit of the temperature of the slurry is preferably 450° C., and more preferably 400° C. In the case where the temperature of the slurry is below the lower limit, the bonds between molecules constituting the coal may not be sufficiently weakened, resulting in a low extraction rate. Conversely, in the case where the temperature of the slurry is above the upper limit, pyrolytic reactions of coal may be very active, and pyrolysis radicals generated in the reactions may recombine, resulting in a low extraction rate.

The slurry obtained in the mixing step is preferably held at the same temperature (extraction temperature) for a certain period of time until the coal components are dissolved. In the case where the pulverized matter is mixed with the extraction solvent in such a manner that the pulverized matter is pressurized and fed into the pipe through which the extraction solvent is flowing, the slurry is preferably fed into an extraction vessel (tank) equipped with a mixer, and then is preferably retained in the extraction vessel for a certain period of time to allow soluble components of coal to be dissolved. The extraction temperature is preferably equal to the temperature of the slurry obtained after the mixing step. For easy control and/or reduction of energy costs, however, the extraction temperature may be slightly different from the temperature of the slurry obtained after the mixing step.

The lower limit of the duration that the temperature is maintained (the extraction time) is preferably 5 minutes, and more preferably 20 minutes. The upper limit of the duration that the temperature is maintained is preferably 3 hours, and more preferably 2 hours. In the case where the duration that the temperature is maintained is shorter than the lower limit, the extraction rate may be insufficient. Conversely, in the case where the duration that the temperature is maintained is longer than the upper limit, extended cycle time may be required, leading to unduly low production efficiency.

It is preferred that the mixing of the pulverized matter with the extraction solvent, and the maintaining of the temperature of the resulting slurry are carried out in a non-oxidizing atmosphere. Specifically, it is preferred that the mixing of the slurry, and the maintaining of the temperature are carried out in the presence of an inert gas such as nitrogen. By using the inert gas such as nitrogen, the slurry is kept from contact with oxygen and thus is prevented from igniting while the mixing is performed and the temperature is maintained.

The pressure at which the pulverized matter is mixed with the extraction solvent and the temperature of the slurry thus obtained is maintained is selected according to the temperature and/or the vapor pressure of the extraction solvent employed, and may be, for example, greater than or equal to 1 MPa and less than or equal to 3 MPa. In the case where the mixing step is performed at a pressure below the vapor pressure, the extraction solvent may volatilize, and thus the soluble components of coal may not be sufficiently extracted. Meanwhile, the extraction with the addition of heat at unduly high pressures causes increases in equipment costs and operating costs associated with production apparatuses.

Solution Separating Step

In Step S4, the solution separating step is performed to separate the slurry obtained after the mixing step, into: a solution containing soluble components of coal dissolved therein; and solid matter containing insoluble components of coal. Although the solution separating step does not require thorough solid-liquid separation, it is desired to separate the largest possible amount of solution containing substantially no solid matter. Examples of the process for separating the solution include gravitational settling, filtration and centrifugal separation. Of these, the gravitational settling, which is suited for continuous treatments, is suitably employed. In the case where the gravitational settling is employed, solid matter in the slurry settles by gravitation, whereby the slurry is separated into a supernatant liquor containing substantially no solid matter and solid-content concentrate containing solid matter having settled therein.

Evaporatively Separating Step

In Step S5, the evaporatively separating step is performed to evaporatively separate the protection solvent and the extraction solvent from the solution separated in the solution separating step, whereby ash-free coal (hyper coal) is obtained.

Examples of the process for evaporatively separating the extraction solvent and the protection solvent from the solution containing soluble components of coal dissolved therein include well-known separation processes such as a distillation process and an evaporation process (e.g. spray drying). After being separated from the solution, the extraction solvent and the protection solvent are recovered in the evaporatively separating step, thereby being repetitively usable as at least a part of a solvent for the extraction solvent and the protection solvent.

The ash-free coal thus obtained has an ash content of 5% by mass or less or of 3% by mass or less, i.e., contains almost no ash matter, with absolutely no moisture. The ash-free coal has a caloric value higher than that of, for example, coal feedstock. Furthermore, the ash-free coal has greatly improved plasticity and fusibility, which is a particularly important quality of coking coal for steelmaking. The ash-free coal exhibits fluidity extremely superior to that of, for example, coal feedstock. The ash-free coal obtained according to the method for producing ash-free coal is therefore suitably used as a coal blend for coke making.

Advantages

Due to involving pulverizing a coal in the presence of the protection solvent in the pulverizing step, the method for producing ash-free coal of the embodiment of the invention enables the particle diameter of the coal to be reduce, while preventing or minimizing aeration of the coal through reduced contact with air. The method thus prevents loss of components to be converted into ash-free coal, and enables the coal to be rapidly heated entirely to its central portion by the heat of the extraction solvent preheated in the mixing step, thereby enabling a relatively high rate of extraction from coal to be achieved. Therefore, the method for producing ash-free coal enables efficient production of ash-free coal.

Other Embodiments

The above-described embodiment does not limit the constituent features of the present invention. Therefore, constituent elements of each part of the above-described embodiment may be omitted, replaced or added based on the description in the present specification and the common technical knowledge, and such omission, replacement and addition should be construed as falling within the scope of the present invention.

EXAMPLES

The present invention will be described below in detail by way of Example. It is to be noted that Example should not be construed as limiting the present invention.

Example

Ash-free coal was prepared as a sample product according to the method for producing ash-free coal of the embodiment of the invention by using, as coal feedstock, bituminous coal that had been subjected to preliminary pulverization to have a mean particle diameter of 0.3 mm, and by using 1-methylnaphthalene as the protection solvent and the extraction solvent.

First, 30 g of the coal was mixed with 20 g of the protection solvent to prepare a pasty mixture. The mixture was charged into a planetary mill, and then was subjected to secondary pulverization, in which coals in the mixture were pulverized to have a mean particle diameter of 0.04 mm. Consequently, pulverized matter in the form of a paste was obtained.

Then, 160 g of the extraction solvent was charged into a heating-and-pressurizing apparatus equipped with a stainless steel filter and having a capacity of 500 cc, where the extraction solvent was heated to 400 ° C. at a pressure of 2.0 MPa.

The pulverized matter was added to the heated extraction solvent, and then, the pulverized matter and the extraction solvent were instantaneously mixed to give a slurry, whose temperature was 380 ° C. The rate of temperature rise of the pulverized matter in this process was about 1,500° C./min.

After being held at 380° C. for 1 hour, the slurry was filtered through the stainless filter of the heating-and-pressurizing apparatus to be separated into: a solution containing soluble components of coal dissolved therein; and filter residues (solid matter), which were undissolved components of coal.

The solution was dried to obtain ash-free coal of Example of the present invention. The filter residues were dried to determine the weight thereof, and thus, the rate of extraction (expressed in % by mass) on a dry ash-free basis (daf) of soluble components from coal in Example of the present invention was determined.

Control Example

As Control Example, ash-free coal was prepared as a sample product according to a conventional production method involving a rapid rise in the temperature of coal. In Control Example, the ash-free coal was prepared as a sample product under the same conditions as those of Example, except that the mixture of coals and the protection solvent was not subjected to the secondary pulverization before use. Then, the rate of extraction of soluble components from coal was determined.

Comparative Example 1

As Comparative Example 1, ash-free coal was prepared as a sample product under the same conditions as those of Example, except that a coal was pulverized to have a mean particle diameter of 0.06 mm in a mortal with no protection solvent charged therein, and thereafter was mixed with the protection solvent to give pulverized matter in the form of a paste. Then, the rate of extraction of soluble components from coal was determined.

Comparative Example 2

As Comparative Example 2, ash-free coal was prepared as a sample product under the same conditions as those of Example, except that a coal was not subjected to the secondary pulverization and thereafter was mixed with 180 g of the extraction solvent at normal temperature to give a slurry, and that the slurry was heated to 380° C. at a rate of temperature rise of 5.5° C./min by the heating-and-pressurizing apparatus and thereafter was held at the temperature for 1 hour. Then, the rate of extraction of soluble components from coal was determined. The production method in this Comparative Example was similar to an ash-free coal production method that had been commonly employed before the establishment of the production method involving a rapid rise in the temperature of coal.

Comparative Example 3

As Comparative Example 3, ash-free coal was prepared as a sample product under the same conditions as those of Example, except that a mixture of a coal and the protection solvent was pulverized into a paste by a planetary mill and thereafter was mixed with 160 g of the extraction solvent at normal temperature to give a slurry, and that the slurry was heated to 380° C. at a rate of temperature rise of 5.5° C./min by the heating-and-pressurizing apparatus and thereafter was held at the temperature for 1 hour. Then, the rate of extraction of soluble components from coal was determined.

Comparative Example 4

As Comparative Example 4, ash-free coal was prepared as a sample product under the same conditions as those of Example, except that a coal was pulverized to have a mean particle diameter of 0.06 mm in a mortal with no protection solvent charged therein and thereafter was mixed with 180 g of the protection solvent at normal temperature to give a slurry, and that the slurry was heated to 380° C. at a rate of temperature rise of 5.5° C./min by the heating-and-pressurizing apparatus and thereafter was held at the temperature for 1 hour. Then, the rate of extraction of soluble components from coal was determined.

FIG. 2 provides a summary of the relationships between the particle diameter and the rate of extraction from coal determined in Example, Control Example, and Comparative Examples 1 to 4.

Comparisons were made among Example, Control Example and Comparative Example 1 that all involved the mixing of a coal in the form of a paste with the extraction solvent so as to rapidly raising the temperature of the coal. The extraction rate determined in Example that involved the secondary pulverization of coal in the presence of the protection solvent was higher than the extraction rate determined in Control Example that did not involve the secondary pulverization. Although the particle diameter was reduced in Comparative Example 1 that involved the secondary pulverization of coal in a state of contacting with air in the absence of the protection solvent, the extraction rate determined in Comparative Example 1 was lower than the extraction rate determined in Control Example.

Control Example, Example and Comparative Example 1 that all involved a rapid rise in the temperature of coal were compared respectively to Comparative Examples 2, 3 and 4 that all involved a slow rise in the temperature of coal. Given the same process for pulverizing the coal, the extraction rate obtained after the rapid rise in the temperature of coal was higher than the extraction rate obtained after the slow rise in the temperature of coal.

Also, comparisons were made among cases that involved a slow rise in the temperature of coal. There was almost no difference in the extraction rates between Comparative Example 2 that did not involve pulverization of coal and Comparative Example 3 that involved pulverization of coal in the presence of the protection solvent. The extraction rate determined in Comparative Example 4 that involved pulverization of coal in the absence of the protection solvent was lower than the extraction rates determined in Comparative Example 2 and Comparative Example 3.

The foregoing results revealed that pulverizing a coal in the presence of the protection solvent prevented loss of soluble components of the coal, and that adding the heated solvent so as to rapidly raise the temperature of the coal yielded enhanced effect of improving the extraction rate.

While the present invention has been described in detail and with reference to the specific embodiment, it would be apparent to one of ordinary skill in the art that various alterations and modifications can be made without departing from the spirit and scope of the present invention.

The present application claims priority to Japanese Patent Application No. 2015-230140, filed on Nov. 25, 2015, and the contents of which are incorporated herein by reference in their entirety.

INDUSTRIAL APPLICABILITY

The method for producing ash-free coal according to the present invention is widely applicable to the production of ash-free coal to be used as, for example, fuels or feedstocks for coke making.

EXPLANATION OF THE REFERENCE SYMBOLS

S1 Pulverizing Step

S2 Heating Step

S3 Mixing Step

S4 Solution Separating Step

S5 Evaporatively Separating Step 

1. A method for producing ash-free coal, comprising: pulverizing a coal in the presence of a protection solvent; heating an extraction solvent; mixing pulverized matter obtained after the pulverizing, with the extraction solvent obtained after the heating; separating a solution containing a coal component dissolved therein, from a slurry obtained after the mixing; and evaporatively separating the protection solvent and the extraction solvent from the solution obtained after the separating.
 2. The method according to claim 1, wherein the pulverized matter obtained after the pulverizing has a mean particle diameter of 0.2 mm or less.
 3. The method according to claim 1, wherein in the mixing, the pulverized matter is mixed with the extraction solvent in such a manner that a temperature of the pulverized matter is raised at a rate of 600° C./min or higher.
 4. The method according to claim 1, wherein the protection solvent and the extraction solvent are identical solvents.
 5. The method according to claim 1, wherein in the pulverizing, a content of the protection solvent in a mixture of the coal and the extraction solvent is greater than or equal to 20% by mass and less than or equal to 60% by mass. 